We have hundreds of raspberry pi s out in the field that experience sdcard failures far too often even though the filesystems are setup as readonly using a ram based overlay filesystem. I suspect something happens during reboot of these pi's and that the SoC generates spurious signals on the bus lines causing havoc with some of the sdcards. It doesn't seem to happen with high end cards or the same setup but with a compute module (which we now use exclusively) with an on board emmc chip.